All of the electric utilities in the Eastern Interconnection are electrically tied together during normal system conditions and operate at a synchronized frequency operating at an average of 60 Hz. The Eastern Interconnection reaches from Central Canada eastward to the Atlantic coast (excluding Quebec), south to Florida, and back west to the foot of the Rockies (excluding most of Texas).

Interconnections can be tied to each other via high-voltage direct currentpower transmission lines (DC ties), or with variable-frequency transformers (VFTs), which permit a controlled flow of energy while also functionally isolating the independent AC frequencies of each side. The Eastern Interconnection is tied to the Western Interconnection with six DC ties, to the Texas Interconnection with two DC ties, and to the Quebec Interconnection with four DC ties and a VFT.